The present invention relates to a device for the sharp-edge illumination of a field of observation lying in a preselectable plane. Such devices are used preferably in combination with a viewing aid, in particular a magnifying viewing aid. Typically, a magnifying viewing aid comprises binocular magnifiers in which a magnifying optical system in a tube is associated with each eye of the observer. By adjusting the angle of convergence of these tubes, such a viewing aid, as known, for instance, from West German Patent Application (Offenlegungsschrift) No. 2,843,835, can be adjusted to different working distances. In order to permit the wearer of such a viewing aid optimal observation, it is important that the field of observation be illuminated as uniformly as possible from the center to the edge, regardless of the working distance selected.
Illuminating systems for viewing aids, particularly magnifying viewing aids, must illuminate the observed field at all times, i.e., they must be worn by the observer in such manner that they participate in all movements of his head and the involved changes in viewing direction. For this reason, the illuminating system is advisedly fastened to a head band or directly to the viewing aid. For example, in the viewing aid known from the said patent application, the illuminating system can be connected directly to the pivot axis.
With such attachment of an illuminating system, there follows a need for the lowest possible weight and the smallest possible development of heat.
It is already known to provide a separate light source and to connect it to the illuminating system via a fiber-optical light guide. This solution has the advantage that the illuminating system which is to be worn by the observer can be made small and lightweight and is thermally decoupled from the light source.
The illuminating system worn by the observer consists, in one such solution, essentially of a mount for the light guide, a collector for focusing the light-emitting surface of the light guide into the plane of observation, and possibly a mirror for reflection of the light.
In a fiber-optical light guide, the light-emitting end surface has a honeycomb structure. Therefore, it is not possible to obtain approximately uniform illumination of the field by forming a real image of this end surface in the observation plane. Recourse is had to selecting the distance between the end surface of the light guide and the collector system in such manner that sharp focusing of the end surface is not obtained in the observation plane. As a result, the honeycomb structure is blurred, but, on the other hand, field illumination materially decreases toward the edge, and blurred-edge limits of such illumination must be tolerated. Such field illumination is not sufficient to meet the demands of use with magnifying viewing aids.